There a bunch of clever guys in this newsgroup, so I though
I'd pose a question that's been bothering me.
OK, first thing, what do "I" mean by engine braking.
Essentially I mean using the engine, via the gearbox, diff, drivetrain
to exert a braking force on the rear wheels (I know it can be front
wheels but we will just consider a RWD car).
We accomplish this by changing down to a lower gear and
re-engaging the clutch at a higher speed than the gear and current
revs would equate to. Thus if we were travelling at 170mph in 5G,
at 9,500 revs and we changed down to 4G we would get engine
braking (and perhaps breaking!).
We wouldn't normally do the above of course, the correct way
to USE engine braking is to brake and change down to a lower
gear at aorund the speed you would be going at max revs in
the lower gear, thus you get good engine braking but shouldn't
damage the engine and shouldn't lock the wheels.
I've used engine braking, in real-life and GPL. I know there are
current F1 drivers using engine braking. The thing is, does it
really help?
Surely if we are braking optimally already, the tires will not accept
any more braking force than we are giving them.
I know engine braking was used in the past as brakes in those
days where simply not powerful enough to give maximum braking
force, that generally is not true of today cars/brakes.
Also, I know that under braking the weight balance of the car
shifts forward considerably. We'd generally set the brake bias
to compensate for that, but we may be able to alter this weight
transfer (as was discussed in gas+brake posts) by using engine
braking, allowing the rear (wider) wheels to come into play more.
Also of course, having engine braking doing some of the slowing
down will alleviate some of the load from the brake pads which
at under very heavy braking will reach very high temperatures at which
they are less efficient.
All that said is there ANY DIFFERENCE, in physics terms between
brakes->pads->disk->hub->wheel->tire than engine->drivetrain->
axle->hub-wheel->tire.
The sort of thing I'm thinking off is, we know that adding power
under braking will negate some of the weight being thrown forward
as we brake. Would braking via the axle lead to a difference in
weight transfer than conventional braking.
Is there any other reason, other than those mentioned above
why engine braking might be more efefctive than conventional
braking?
TIA
Maxx